Pen cap



FIG. 1 is a side elevational view of a pen cap showing my new design;

FIG. 2 is a front elevational view;

FIG. 3 is a rear elevational view;

FIG. 4 is a top plan view on an enlarged scale; and

FIG. 5 is a bottom plan view on an enlarged scale. 

The ornamental design for a pen cap, as shown and described. 